#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
int main() {
    int score = 0;
    scanf("%d", &score);
    if (score <= 100 && score >= 0)
    {
        if (score >= 90)
        {
            printf("A\n");
        }
        else if (score >= 80 && score < 90)
        {
            printf("B\n");
        }
        else if (score >= 70 && score < 80)
        {
            printf("C\n");
        }
        else if (score >= 60 && score < 70)
        {
            printf("D\n");
        }
        else (score < 60 && score >= 0)
        {
            printf("E\n");
        }
    }
    else {
        {
            printf("F\n");
        }
    }
    return 0;
}